Continuous casting mold venting apparatus



NOV- 22, 1966 J. E. DORE r-:TAL

CONTINUOUS CASTING MOLD VENTING APPARATUS Filed oct. 22. 1963 INVENTORS`JAMES E. DORE AVERY L. KEAR/VEV United States Patent 3,286,310CONTINUOUS CASTING MOLD VENTING APPARATUS James E. Dore, Milford, Conn.,and Avery L. Kearney,

Birmingham, Mich., assignors to Olin Mathieson Chemical Corporation, acorporation of Virginia Filed Oct. 22, 1963, Ser. No. 317,883 5 Claims.(Cl. 22-57.2)

This invention relates to improvement-s in apparatus and method ofcontinuous casting of metals and more particularly to an improvedcontinuous casting mold which provides for the escape of gases or vaporscreated during the casting process, and to the method of vapor removal.

In the art of continuous casting, many advantages have been derived bydisposing the longitudinal axis of the mold in a horizontal orientationso that the casting of the ingot takes place in a horizontal directionfrom the inlet end of the mold to the outlet end thereof. One of theseis that in casting continuously, ingots of great length can be formedwithout the need for deep pits or other facilities which would berequired to receive or handle vertically oriented lengths of ingot.Also, horizontal casting facilities higher production speed as a resultof the elimination of casting interruptions inherent in vertical castingtechniques due to the nite lengths of ingot which can be formed withoutremoval of these lengths from the casting apparatus.

Production speed, with acceptable quality being understood, is the mostimportant test of a casting process in industrial application. Effortsto increase the output from a casting machine and/ or to reduce themanpower needed to make a given quantity of cast metal are important forthe economic feasibility of a particular casting machine or process.

One of the primary factors preventing attainment of higher castingspeeds in the horizontal continuous casting of aluminum alloys and othernon-ferrous metals is nonuniform heat removal in the mold. This problemhas been traced to a vapor barrier or bubble in the top of the moldcavity which is formed by the vaporization of mold lubricant and/orentrapment of air at the start of the cast. The vapor barrier greatlyreduces heat transfer from the molten metal to the mold wall andproduces a nonsymmetrical solidication front and a weak zone in the topof the forming embryo ingot shell. Casting speed, of course, is limitedby the ability of this shell to contain the still liquid metal at thecenter of the casting as the ingot emerges from the mold.

It is well known in the casting art that one of the principal causes offailure in the continuous direct chill casting of metal is the frictionbetween the work and the casting die, and/or wetting of the casting dieby the molten metal which produces welding of the ingot shell to themold and gauling. It is accordingly a conventional practice to apply 4alubricating medium, generally oil, to the interface between the ingotshell and mold during the solidication stage of the casting process. Agreat variety of processes and apparatuses are present in the castingart for applying the lubricant to the ingot-mold interface lat somepoint within or adjacent to the ca-sting mold. The amount of lubricantused and the point of introduction are both critical factors inconventional processing, and little or no casting difficulty isencountered if these factors are very -closely controlled. However, suchclose control is difficult to maintain and frequently cannot be achieveddue to the many variable circumstances which enter into castingpractice. The difficulty, of which it is the basic object of thisinvention to overcome, is the creation of the aforementioned vaporbarrier or bubble formed by the almost instantaneous vaporiza- 3,286,310Patented Nov. 22, 1966 tion of an excess of lubricant when it contactsthe extremely hot surface of the forming ingot, or when lubricant is notintroduced at the correct point. The removal of the top gaseous layersin the mold resulting from this lubricant vaporization, or from airentrapment in the mold by the molten metal at the start of casting,broadens the range of operating parameters and makes lubrication lesscritical, and is essential for uniformity of heat removal in thehorizontal casting process. It has been found that a thin gas layer,even on the order of a thousandth of an inch in thickness, can be acontrolling resistance to heat conduction and extraction.

This invention provides improved mold constructions which allow thehorizontal continuous casting of aluminum alloys and other non-ferrousalloys at speeds substantially higher than those presently possible.These constructions provide for escape of vapor gases trapped in themold cavity to insure uniform heat removal from the molten metal to themold Wall thereby resulting in a more symmetrical solidification of theforming embryo ingot shell.

The mold designs of this invention comprise generally an elongate moldof varying cross section having a mold cavity an inlet for molten metalat one end and an outlet for the solidified ingot at the other. The moldcavity is surrounded by a chamber or area for the association therewithof a cooling means, which may take the form of spray quenching apparatusor a simple cooling medium circulation means, either of whichfacilitates a high rate of heat removal from the mold wall which in turninduces rapid solidification of the molten metal within 4the moldcavity. Means are provided to control the rate of flow of molten metalinto the mold, land means are also provided for withdrawing the solidtedingot from the discharge end of the mold.

The improvement of this invention consists generally of providing anescape route for the gases or vapors that accumulate in the mold cavity.This escape route is preferably located around or adjacent the upperportion of the mold, and Aat least at the inlet end thereof, andcomprises generally a ported distribution nozzle or ported mold wall,either of which communicates with a vapor collection plenum which inlturn connects with a vacuum system to assist in the removal of vaporscollected in the plenum.

Having thus described the .invention in a general manner, it is aprimary object thereof to provide a mold design for continuous casting.apparatus which eliminates the aforementioned vapor barrier problem andthus allows substantially higher casting speeds.

It is another object of this invention to provide a horizontalcontinuous casting mold which will eliminate even an extremely thin gasfilm surrounding the solidifying ingot so as to improve ingot to moldheat transfer and consequently increase casting speeds.

It is yet another object of this invention to provide a horizontalcontinuous casting apparatus which provides a vapor escape route forvapors or bubbles created in the mold by vaporization of mold lubricantand/or entrapment of air.

It is still another object of the present invention to provide ahorizontal continuous casting apparatus having vapor escape meanscommunicating directly with the ingot-mold interface at the location ofhighest vapor or air concentration.

It is still another object of the present invention to provide ahorizontal continuous casting apparatus in which a vacuum system is incommunication with the areas of highest vapor concentration within themold to facilitate the vapor removal.

It is still another object of the present invention to providehorizontal continuous casting apparatus which is simple in construction,efiicient in operation and economical to manufacture and maintain.

It is still another object of the present invention to provide a methodof continuous casting which achieves removal of vapor or gases createdin the casting process.

These and other objects and advantages of the invention will be morereadily apparent from a consideration of the following detaileddescription when read in conjunction with the laccompanying drawings, inwhich:

FIGURE 1 is a vertical sectional view of one embodiment of the inventionillustrating the mold and vapor release means during the solidicationstage of the casting process;

FIGURE 2 is a vertical sectional view taken on line 2 2 of FIGURE 1;

FIGURE 3 is a view similar to FIGURE 1 illustrating another embodimentof the invention;

FIGURE 4 is a view similar to FIGURES 1 and 3 illustrating still anotherembodiment of the invention;

FIGURE 5 is a vertical sectional view on the line 5-5 of FIGURE 4; and

FIGURE 6 is a partial sectional view similar to FIG- URE 5, illustratinga further embodiment thereof.

Referring now to FIGURES 1 and 2, wherein one embodiment of theinvention is illustrated, the reference numeral 10 indicates generally ahorizontal casting apparatus comprising a substantially cylindricalhollow casting mold 12 having inner and outer walls 14 and 16,respectively, which define .a chamber 18 for the circulation therein ofa cooling medium 20. Generally, the cooling medium is water, either latroom temperature or at some elevated temperature depending upon variouscharacteristics of the casting process, although other cooling media maybe used. The cooling medium 20 enters through an inlet port 22,circulates Within the chamber 18 and all 'or a portion of it iswithdrawn through an exit port (not shown).

The discharge end of the casting mold 12 is provided with a plurality ofapertures 24 through which a portion being utilized.

The mold 12 is further provided with a ported distribution nozzle 28having a molten metal inlet end 30 for the introduction of the moltenmetal into the casting mold. The distribution nozzle 28 has an outwardlytapered surface 32 which terminates at 34 adjacent the inlet end of thecasting mold 12. It will be observed from FIG- URE 1 that the terminalportion 34 has an outward flare or taper which is much steeper in degreethan the tapered surface 32 which extends over a major portion of thelength of the distribution nozzle 28. It is to be understood that thisnozzle configuration is merely illustrative of a variety of nozzledesigns which may be utilized with the present invention.

Molten metal is fed into the distribution nozzle through any suitableflow control means, and passes from the distribution nozzle into themold chamber 34 defined by the interior surface of the inner mold wall14. As the molten metal passes through this chamber, solidificationthereof commences adjacent the inner surface of the mold wall 14 andcontinues through the mass of molten metal toward the center thereof,thereby forming the crater 36 of molten metal surrounded by an annularshell 38 of solidified metal.

In order to provide an escape route for the gases or vapors thataccumulate in the mold chamber or cavity,

nozzle 28 is provided with a plurality of radially extending vaporescape ports 40 which connect interiorly in the flared portion 34 of thedistribution nozzle located immediately adjacent the inlet end of thecasting mold 12, and which extend rearwardly therefrom for a shortdistance and then outwardly to the outer surface 42 of the distributionnozzle. As will be seen from FIGURE 2, the ports 40 are distributedradially around approximately the upper half of the distribution nozzle,although more or less of the circumferential extent of the distributionnozzle may be provided with vapor escape ports depending upon the amountof lubricant used, the point or method of introduction, and extent ofvaporization of mold lubricant or gas or Aair entrapment encountered inthe particular casting apparatus to which the invention is applied.

While the escape ports 40 may in some instances be sufficient ofthemselves to provide adequate vapor removal, it is desirable to assureremoval of as much as possible of the vapor or gases in order to reduceto a minimum, if not eliminate, the heat transfer barrier which thevapor or gases create. To facilitate vapor removal, the escape ports 40communicate with a collection plenum 42 which illustratively comprises-a semicylindrical hood 44 having outlet means 46 adapted to beconnected to a vacuum system providing a reduced pressure within thecollection plenum of approximately 5 to 125 millimeters of mercury belowatmospheric pressure. The molten metal static head, the amount and typeof lubricant used, land the point of lubricant introduction into themold are among the factors which determine the extent of vacuummaintained in the plenum.

It should be noted that the ports 40 must be of such a size that thesurface tension of the molten metal will be sufficient to prevent themetal from entering the ports and either solidifyi-ng therein, therebyblocking the passage of vapors to the collection plenum 42, or beingdrawn by the reduced pressure into the collection plenum 42 andsolid-ifying therein. At the same time, the ports 40k must not be ofsuch small size as to prevent free passage of the vapors from the moldcavity to the collect-ion plenum 42.

The extent of sircumferential coverage of the ports 40, the numberprovided, and the diameter of the ports are all variables which are`determined by the vapor circulation or gas or air entrapmentcharacteristics of the particular casting apparatus being utilized.Accordingly, these features of the vapor escape means will vary from oneinstallation to another.

A second embodiment of the invention is illustrated in FIGURE 3 in whichthe mold is constructed to have the vapor escape means as an integralpart of the mold. More specifically, the mold 1-12 is again divided withinterior and exterior concentric walls 114 and 116, respectively, toprovide a circulation chamber 118 for the cooling medium 120 whichenters through the port 122 and circulates within chamber 118 and exits,at least in part, through ports 124 to provide direct cooling effectupon the solidifying portion of the ingot 126. Molten metal isintroduced int-o the mold through distribution nozzle 128, the inlet endof which is associated with appropriate flow control means.

In this embodiment of the invention the inner wall 114 is provided witha continuous slot Ior annulus 146, or, if desirable, an annular seriesof closely spaced radially extending apertures, which communicatesbetween the mold cavity 134 defined by the inner surface of wall 114 anda collection plenum 142 defined by extensions of inner and outer moldwalls 114 and 116, an annular partition wall 117 and the end wall 119 ofthe mold 112. The collection plenum 142 is connected by means of outlet146 to a suitable vacuum system as described above in connection withFIGURES 1 and 2. The annulus or slot 140 may be continuous .around themold wall 114, or it may be confined to as l-ittle as the top 60' of themold, again depending upon the same factors mentioned above regardingthe circumferential extent of ports 40 in distri- -bution nozzle 28. Itshould also be noted that the annulus or slot 140, or the apertures asthe case may be, must be of such a size that surface tension of themolten metal will prevent entry thereof into the slot or passagetherethrough into the collection plenum in order to prevent thedeleterious effects which this would have upon the vapor escape meansand upon the casting itself.

Still another embodiment of the invention is illustrated in FIGURES 4and 5 which includes casting mold 2112 having inner and outer concentricwalls 214 and 21-6, respectively, defining the circulating chamber 218for a cooling medium 220 which enters through entrance port 222 andexits through the apertures 224 for direct cooling of the solidifyingportion of ing-ot 226. Distribution nozzle 228 receives molten metal atits inlet end 230 from a flow control means and discharges the moltenmetal into the inlet end of mold 212.

The vapor escape means of this embodiment comprises a series of closelyspaced ports or holes 240 which are disposed in a single row located inthe uppermost part of the mold and extending substantially from one endof the casting mold to the other. This vapor escape route may also, ifdesirable, take the form of a continuous slot rather than the series ofholes illustrated in FIGURE 4. The holes or slot communicate between theinterior of the mold cavity and a collection plenum 242 which is denedin part by a hood 244 mounted on the upper portion of exterior mold wall216, and in part by a pair of upstanding longitudinally extending Walls221 and 223 respectively which interrupt the continuity of thecirculation chamber 218 along the upper port-ion of the mold 212. Thecollection plenum 242 is provided with an outlet port 246 which issuitably connected to a vacuum system in orde-r to maintain a reducedpressure in the collection plenum to assist in the removal of vapors andgases.

It is to be noted that this embodiment of the invention offers anadvantage over those previously described in that it allows vapor to becollected along the entire length of the mold. Thus, no isolated bubblesor vapor pockets can be formed and exist some distance from the inletend of the mold and not be accessible to the vapor escape ports locatedat the inlet end of the mold. Also, in the case of the slot, problemsassociated with the entry and freezing of metal in the vapor escapeports is minimized. Since the slot is parallel to the direction ofcast-ing, any metal that flashes into the slot will be withdrawn withthe ingot thus making the slot self cleaning.

AIt should again be remembered that the holes 240, or in the alternativethe continuous slot, must be small enough to prevent the entry of moltenmetal therein.

Further modifications which are deemed to be within the scope of theinvention are suggested .by refe-rence to the accompanying drawings. Forexample, referring to FIGURE l in place of the ported distributionnozzle sh-own therein, a non-ported nozzle may be substituted which isfabricated from a porous material, the material being of such porositythat the accumulated vapor-s or gases will pass therethrough but moltenmetal will not. Additionally, a porous metal ring or insert may beplaced within the upper portion of the nozzle 28 of FIGURE 1 in place ofthe apertures 40 in order to provide a vapor escape route, in which casethe nozzle 28 would be fabricated of non-porous material.

In either of these embodiments, a collection plenum is utilized tofacilitate removal of the vapors, the plenum, in the case of the porousnozzle, covering substantially the entire nozzle.

Among the materials su-itable, either for the porous nozzle or for theporous insert or ring for use with a nonporous nozzle are the following:porous carbon, cellular silicon carbide, other cellular or porousceramic and refractory materials resistant to melting and attack bymolten metals.

Referring to FIGURES 3 and 4 it is also contemplated that a porous metalinsert be substituted for the continuous annulus of FIGURE 3 or the rowof holes 240 of FIGURE 4. The latter expedient is illustrated in theenlarged partial sectional view of FIGURE 6, analogous to FIGURE 5 withanalogous structure 214, 2.16, 220, 221, and 223 indicated by the samereference characters primed. Instead of employing holes 240, there isprovided a continuous slot 340, in which may be situated a suitablyshaped porous metal insert 341.

It will .be apparent fr-om the foregoing description and accompanyingdrawings that there has been provided an improved mold for high speedhorizontal continuous casting which is believed to provide a solution tothe foregoing problems and achieve the aforementioned objects. It is tobe understood that the invention is not limited to the illustrationsdescribed and s-hown herein which are deemed to be merely illustrativeof the best modes of carrying out the invent-ion, and which aresusceptible of modification of form, size, arrangement of parts anddetail of operation, but rather is intended to encompass all suchmodifications as are within the spirit and scope of the invention as setforth in the appended claims.

What we claim and desire to secure by Letters Patent is:

1. Casting apparatus comprising:

(A) an elongate mold having a Wall defining a molten metal solidiicationcav-ity therewithin, said mold hav-ing (1) an inlet .and an outlet endand (2) cooling means disposed in heat transfer relationship with saidcavity for rapidly inducing so'l-idification of molten metal Within saidcavity,

(B) `a distribution nozzle associated with said inlet end of said mold,

(C) vapor escape means disposed in said mold and communicating betweensaid mold cavity and arnbient atmosphere for removing vapor or gasesfrom said solidiiication cavity formed during solidification of moltenmetal therewithin whereby said cooling means is in more effective heattransfer relationship with said solidifying metal, and

(D) a collection plenum communicating with said vapor escape means andmaintained at a subatmospheric pressure, said collection plenumcomprising an elongate chamber overlying said vapor escape means andtraversing the longitudinal extent of said mold cavity, said chamberbeing deiined by integral radial extensions of said mold wall.

2. Casting apparatus as set forth in claim 1 wherein said vapor escapemeans comprises a passageway extending through said mold wall andcommunicating with at least said inlet end of said mold cavity.

3. Casting apparatus as set forth in claim 2 wherein said passagewaycomprises a plurality of longitudinally aligned lholes formed in anupper portion of said mold wall.

4. Casting apparatus as set forth in claim 2 wherein said passagewaycomprises a longitudinally extending slot disposed in the uppermostportion of said mold wall.

5. Casting apparatus as set forth in claim 2 wherein said passagewaycomprises a longitudinally extending porous metal insert disposed in theuppermost portion of said mold Wall.

References Cited by the Examiner UNITED STATES PATENTS 3,022,552 2/ 1962Tessmann 22-572 FOREIGN PATENTS 814,435 6/ 1959 Great Britain.

I SPENCER OVERHOLSER, Primary Examiner.

R. S. ANNEAR, Assistant Examiner.

1. CASTING APPARATUS COMPRISING: (A) AN ELONGATE MOLD HAVING A WALLDEFINING A MOLTEN METAL SOLIDIFICATION CAVITY THEREWITHIN, SAID MOLDHAVING (1) AN INLET AND AN OUTLET END AND (2) COOLING MEANS DISPOSED INHEAT TRANSFER RELATIONSHIP WITH SAID CAVITY FOR RAPIDLY INDUCINGSOLIDIFICATION OF MOLTEN METAL WITHIN SAID CAVITY, (B) A DISTRIBUTIONNOZZLE ASSOCIATED WITH SAID INLET END OF SAID MOLD, (C) VAOR ESCAPEMEANS DISPOSED IN SAID MOLD AND COMMUNICATING BETWEEN SAID MOLD CAVITYAND AMBIENT ATMOSPHERE FOR REMOVING VAPOR OR GASES FROM SAIDSOLIDIFICATION CAVITY FORMED DURING SOLIDIFICATION OF MOLTEN METALTHEREWITHIN WHEREBY SAID COOLING MEANS IS IN MORE EFFECTIVE HEATTRANSFER RELATIONSHIP WITH SAID SOLIDIFYING METAL, AND (D) A COLLECTIONPLENUM COMMUNICATING WITH SAID VAPOR ESCAPE MEANS AND MAINTAINED AT ASUBATMOSPHERIC PRESSURE, SAID COLLECTION PLENUM COMPRISING AN ELONGATECHAMBER OVERLYING SAID VAPOR ESCAPE MEANS AND TRAVERSING THELONGITUDINAL EXTENT TO SAID MOLD CAVITY, SAID CHAMBER BEING DEFINED BYINTEGRAL RADIAL EXTENSIONS OF SAID MOLD WALL.